If i take an antihistamine, would this stop an allergic reaction? (if taken 30mins/1hr beforehand with enough time to take effect)

Prevent allergic rxn: Don't count on it. That might work, but it could be very dangerous--fatal! you need tests to determine your allergies and if you want to challenge yourself after that, you should do it in an allergist's office. Better idea: take shots for inhalant allergies that cross react with foods and then retest the foods. The level of allergy could decrease, making it safer for you to eat the fruit again.